Shock ages of meteorites

Isotopic chronometers can provide information about the collisional history of the meteorite parent bodies. As discussed in Chapter 8, isotopic chronometers can give the time of 

Chronology of the solar system from radioactive isotopes 

The majority of HED meteorites show evidence of isotopic resetting over a limited period of time between 3.4 and 4.1 Ga ago. Most of the evidence comes from the system, but the 87Rb-87Sr system was also disturbed at this time in some meteorites 

In a limestone deposit at Kinnekulle, Sweden, a remarkable collection of more than 40 highly altered meteorites (Fig. 9.18) totaling 7.7 kg have been collected during routine guarrying operations (Schmitz etal., 1997,2001,2003). The 3.2-m-thick limestone layer in which they are found was deposited over -1.75 Myr in the mid-Ordovician. Despite being almost completely replaced by calcite, barite, and phyllosilicates, the meteorites are easily identified by their chondritic texture. Their identification as meteorites is confirmed by measurements of platinum-group elements. The chemical characteristics of relict spinels indicate that they are either L or LL chondrites. 

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